IAP/RAS, Nizhny Novgorod, Russia
Euclid TechLabs, LLC, Solon, Ohio, USA
UNN, Nizhny Novgorod, Russia
We propose an efficient XFEL consisting of sequential RF undulator sections using: 1) tapered flying RF undulators, 2) short pulse, high peak-power RF and 3) driving undulator sections by spent electron beam. In a flying RF undulator, an electron bunch propagates through a high-power, nanosecond, co-propagating RF pulse. Helical waveguide corrugation supports a space harmonic with a negative propagation constant, providing a large Doppler up-shift. The undulator tapering technique improves FEL efficiency by 1-2 orders of magnitude in comparison with other facilities by decreasing the undulator period so that particles are trapped in the combined field of the incident x-ray and undulator field. We develop a so-called non-resonant trapping regime not requiring phase locking for feeding RF sources. Simulations show that by decreasing the corrugation periodicity one can vary an equivalent undulator period by 15%. The spent electron beam can be used to produce wakefields that will drive the RF undulator sections for interaction with the following beam. We have already manufactured and tested the 30 GHz simplified version of the 50 cm long undulator section for cold measurements.
